mysql中条件查询加排序和索引的关系

ikjhgf

跟一个朋友，不错公司的主管交流时，对于mysql中条件查询和排序时 与索引的关系
mysql> explain select * from article where title='希望光伏企业挺过2个月' o
rder by id desc\\\\\\\\G
*************************** 1. row ***************************
           id: 1
  select_type: SIMPLE
        table: article
         type: index
possible_keys: NULL
          key: PRIMARY
      key_len: 4
          ref: NULL
         rows: 567
        Extra: Using where
1 row in set (0.00 sec)

mysql> select * from article where title='希望光伏企业挺过2个月';
+----+-------------+---------+--------+-----------------------------+----------+
-----------+-------+-------------+---------+---------+--------------------------
--------------------------------------------------------------------------------
--------------------------------------------------------------------+--------+--
---------+--------+------------+------------+
| id | category_id | user_id | app_id | title                       | subtitle |
professor | money | cooperation | project | address | discription

                                                                    | source | r
ecommend | status | ctime      | mtime      |
+----+-------------+---------+--------+-----------------------------+----------+
-----------+-------+-------------+---------+---------+--------------------------
--------------------------------------------------------------------------------
--------------------------------------------------------------------+--------+--
---------+--------+------------+------------+
| 10 |           2 |       4 |      0 | 希望光伏企业挺过2个月 |          |
           |     0 |             |         |         | 希望企业挺过两个月。 |        |
        1 |      0 | 1371524848 | 1371525226 |
+----+-------------+---------+--------+-----------------------------+----------+
-----------+-------+-------------+---------+---------+--------------------------
--------------------------------------------------------------------------------
--------------------------------------------------------------------+--------+--
---------+--------+------------+------------+
1 row in set (0.00 sec)

mysql> explain select * from article where title='希望光伏企业挺过2个月';
+----+-------------+---------+------+---------------+------+---------+------+---
---+-------------+
| id | select_type | table   | type | possible_keys | key  | key_len | ref  | ro
ws | Extra       |
+----+-------------+---------+------+---------------+------+---------+------+---
---+-------------+
|  1 | SIMPLE      | article | ALL  | NULL          | NULL | NULL    | NULL |  5
67 | Using where |
+----+-------------+---------+------+---------------+------+---------+------+---
---+-------------+
1 row in set (0.00 sec)